This disclosure relates generally to a catalytic conversion process for reducing carbon oxides to a valuable solid carbon product and, in particular, to the use of carbon oxides (e.g., carbon monoxide and carbon dioxide) as the primary carbon source for the production of solid carbon products (such as Buckminster fullerenes) using a reducing agent (such as hydrogen or a hydrocarbon) typically in the presence of a catalyst. This method may be used for commercial manufacture of solid carbon products in various morphologies and for catalytic conversion of carbon oxides to solid carbon and water.
These methods produce carbon products from carbon oxides. The methods produce carbon products, such as Buckminster fullerenes, using carbon oxides as the primary carbon source. The methods thus involve catalytic conversion of carbon oxides (primarily carbon monoxide and carbon dioxide) to solid carbon and water. The methods may use the atmosphere, combustion gases, process off-gases, well gas, and other natural and industrial sources of carbon oxides. The carbon oxides may be separated from these sources and concentrated as needed.
Solid carbon has numerous commercial applications. These applications include longstanding uses such as uses of carbon black and carbon fibers as a filler material in tires, inks, etc., many uses for various forms of graphite (such as the use of pyrolytic graphite as heat shields), and innovative and emerging applications for Buckminster fullerenes (including buckyballs and buckytubes). Prior methods for the manufacture of various forms of solid carbon typically involve the pyrolysis of hydrocarbons (often natural gas) in the presence of a suitable catalyst. The use of hydrocarbons as the carbon source is due to historically abundant availability and low cost of hydrocarbons. The use of carbon oxides as the carbon source in reduction reactions for the production of solid carbon has largely been unexploited.
The present process uses two abundant feedstocks, carbon oxides (e.g., carbon dioxide (CO2) and carbon monoxide (CO)) and a reducing agent. The reducing agent is preferably a hydrocarbon gas (e.g., natural gas, methane, etc.), hydrogen (H2) gas or a mixture thereof. A hydrocarbon gas serves the dual function as both an additional carbon source and as the reducing agent for the carbon oxides. Syngas comprises primarily carbon monoxide (CO) and hydrogen (H2) so that the gas has both the carbon oxide and the reducing gas in mixture. Syngas may be profitably used as all or a portion of the reaction gas mixture.
Carbon oxides, particularly carbon dioxide, are abundant gases that may be extracted from point source emissions, such as the exhaust gases of hydrocarbon combustion, and from some process off gases. Carbon dioxide may also be extracted from the air. Because point source emissions have much higher concentrations of carbon dioxide than air, they are often economical sources from which to harvest the carbon dioxide. However, the immediate availability of air may provide cost offsets by eliminating transportation costs through local manufacturing of the solid carbon products from carbon dioxide in air.
Carbon dioxide is increasingly available and inexpensive as a byproduct of power generation and chemical processes where the object is to eliminate the emission of carbon dioxide to the atmosphere by capturing the carbon dioxide and subsequent sequestration (often by injection into a geological formation). The capture and sequestration of carbon dioxide is the basis for “green” coal fired power stations, for example. In current practice, capture and sequestration of the carbon dioxide entails significant cost. The process disclosed herein considers the carbon dioxide as an economically valuable co-product instead of an undesirable waste product with associated disposal costs.
The methods disclosed may be incorporated into power production and industrial processes for sequestration of carbon oxides and converting them to valuable solid carbon products. For example, the carbon oxides in the combustion or process off-gases may be separated and concentrated to become a feedstock for this process. In some cases these methods may be incorporated directly into the process flow without separation and concentration, for example, as an intermediate step in a multi-stage gas turbine power station. The direct incorporation into the process flow is particularly suitable for oxy-combustion processes.
The present catalytic conversion process may be incorporated with fossil fuel combustion processes. Many methods for integrating the catalytic conversion process with various combustion processes and power production cycles will readily occur to the skilled practitioner. These methods include adding a catalytic converter between stages in a power production cycle so that the combustion gases are passed through a catalytic converter and at least some portion of the constituent carbon oxides in the combustion gases are converted to solid carbon, or separating the carbon oxides from all, or a portion of, the combustion process effluent gases and routing the separated gases through the catalytic converters.
Combing the catalytic conversion process with a separation process may be beneficial because it would deliver a carbon separation and sequestration unit that may be more economical than existing separation and sequestration methods. The operating efficiencies may arise from the fact that the catalytic converters may use low pressure carbon oxides, so the equipment and costs associated with compression, liquefaction and transport are reduced, and from the use of the heat produced in the catalytic converters to provide at least some of the process heat for the separation process. Specific methods for combining catalytic converters with various separation processes will readily occur to the skilled practitioner. For example, a separation process, such as amine absorption, may receive at least part of the heat required for desorption from the catalytic converter, and deliver low pressure carbon oxide gases to the catalytic converter.
There are a limited number of ways that carbon, oxygen, and hydrogen can react. There is a spectrum of reactions involving these three elements wherein various equilibria have been named. Hydrocarbon pyrolysis is the range of equilibria between hydrogen and carbon that favors solid carbon production, typically with little or no oxygen present. The Boudouard reaction, also called the carbon monoxide disproportionation reaction, is the range of equilibria between carbon and oxygen that favors solid carbon production, typically with little or no hydrogen present. The Bosch reaction is the region of equilibria where all of carbon, oxygen, and hydrogen are present that favors solid carbon production. Other equilibria favor the production of carbon oxides or hydrocarbons (e.g., the Sabatier and the Fischer-Tropsch processes) with no solid carbon product.
The relationship between the hydrocarbon pyrolysis, Boudouard, and Bosch reactions may be understood in terms of a C—H—O equilibrium diagram, as shown in FIG. 21. The C—H—O Equilibrium Diagram of FIG. 21 shows various known routes to carbon nanotube (“CNT”) formation. The hydrocarbon pyrolysis reactions are on the equilibrium line that connects H2 and C, the left side of the triangle. The names on this line are of a few of the researchers who have published results validating CNT formation at various points on this line. Many patents have been issued for the use of the hydrocarbon pyrolysis reaction in the production of CNTs. The Boudouard or carbon monoxide disproportionation reactions are on the equilibrium line that connects O2 and C, right side of the triangle. The equilibrium lines for various temperatures that traverse the diagram show the approximate regions in which solid carbon will form. For each temperature, solid carbon will form in the regions above the associated equilibrium line, but will not form in the regions below the equilibrium line.
The present methods, based generally on the Bosch reaction, are in the interior region of the triangle where equilibrium is established between solid carbon, hydrogen, and oxygen in various combinations. What is disclosed here is that the central region has several points that in fact are highly favorable for the formation of CNTs and several other forms of solid carbon product, and that through careful selection of the catalysts, reaction gases, and reaction conditions, the type of solid carbon produced can be selectively controlled. Thus these methods open new routes to the production of valuable solid carbon products such as CNTs.
The Ellingham diagram defines the equilibrium formation enthalpy of solid carbon from carbonaceous gases as a function of temperature. This diagram is well known to the art and is a useful reference in understanding this range of equilibria.
The methods of the present invention employ the Bosch reaction to produce valuable solid carbon products. The Bosch reaction (CO2+2H2⇄Csolid+2H2O) reduces carbon dioxide with hydrogen for the production of solid carbon and water. The temperatures for the Bosch reaction reported in the literature range from 450° C. to over 2000° C. The reaction rates are typically enhanced and reaction temperatures reduced by the use of a catalyst such as iron.
Previously, the Bosch reaction was used with the objective of recovering oxygen from respiratory processes in enclosed isolated environments such as submarines, spacecraft and lunar or Mars bases (see, for example, U.S. Pat. No. 4,452,676, “Carbon Dioxide Conversion System for Oxygen Recovery,” Birbarta et al.; and U.S. Pat. No. 1,735,925, “Process of Producing Reduction Products of Carbon Dioxide,” Jaeger). Typically, the solid carbon form is specified as graphite deposited on a solid catalyst bed or collection plate, and is noted as a nuisance that fouls the catalyst and must be disposed of There is little previous disclosure of the various forms of solid carbon that might be produced through modifications to this process, or of solid carbon as the principal desired product of these reactions.
The Boudouard reaction is also called the carbon monoxide disproportionation reaction and it proceeds as:2CO(g)C(s)+CO2(g), ΔH=−169 kJ/mol of solid carbonThe present method differs from Boudouard reaction in at least three ways: i) carbon monoxide is not necessary to the method, though it may be used as a carbon source; ii) a separate reducing agent is used to reduce the carbon monoxide to solid carbon and water; and iii) carbon dioxide is not a product of the reaction.
A recent set of patents discloses the use of carbon monoxide as the carbon source for the formation of carbon nanotubes. The production of solid carbon from carbon monoxide is via the carbon monoxide disproportionation or Boudouard reaction. Smalley (U.S. Pat. No. 6,761,870) discloses the use of the carbon monoxide disproportionation reaction in the presence of a catalyst in Gas-phase nucleation and growth of single-wall carbon nanotubes from high pressure CO for the production of single-walled carbon nanotubes.
“A Novel Hybrid Carbon Material,” Nasibulin et al. (Nature Nanotechnology 2, 156-161, 2006) discloses the formation of what they term nanobuds in two different one-stop continuous methods, during which fullerenes were formed on iron-catalyst particles together with SWNTs (single-walled nanotubes) during carbon monoxide disproportionation. This use of carbon monoxide disproportionation is typical of the literature. Nasibulin further discloses in “An essential role of CO2 and H2O during single-walled CNT synthesis from carbon monoxide” (Chemical Physics Letters 417 (2005) 179-184) the important influences of carbon dioxide and water in the growth of carbon nanotubes, but specifically notes that at concentrations above about 15,000 ppm, the presence of CO2 inhibits the formation of carbon nanotubes.
Tennent in U.S. Pat. No. 4,663,230, “Carbon Fibrils, Method for Producing Same and Compositions Containing Same” discloses and does specify the use of carbon oxides in the production of carbon fibrils, though his reaction is specified as a reaction between the carbon-containing compound and the carbon in the specially prepared catalyst of his invention, where the catalyst was essentially a carbon particle coated with a suitable metal. Tennent specifically claims “wherein the compound capable of reacting with carbon is CO2, H2 or H2O.”
Resasco et al. (U.S. Pat. No. 6,333,016) in “Method of Producing Carbon Nanotubes,” discloses carbon monoxide disproportionation in the presence of various Co:Mo catalysts. They make no claims with regard to the use and presence of a reducing agent in the reaction gas mixture.
In contrast, the present method is not limited to carbon monoxide as the carbon source gas. The present method uses a reducing agent other than a carbon oxide. Also, the present method relies on the mixing of the carbon oxide with a reducing agent in the presence of a catalyst for the production of the valuable solid carbon product.
Hydrocarbon pyrolysis is known and is commercially used in the production of carbon black and various carbon nanotube and Buckminster fullerene products. Various methods exist for creating and harvesting various forms of solid carbon through the pyrolysis of hydrocarbons using temperature, pressure, and the presence of a catalyst to govern the resulting solid carbon morphology. For example, Kauffman et al. (U.S. Pat. No. 2,796,331) discloses a process for making fibrous carbon of various forms from hydrocarbons in the presence of surplus hydrogen using hydrogen sulfide as a catalyst, and methods for collecting the fibrous carbon on solid surfaces. Kauffman also claims the use of coke oven gas as the hydrocarbon source.
Wiegand et al. (U.S. Pat. No. 2,440,424) disclose an improved process for the manufacture of carbon black that comprises rapidly and thoroughly admixing a hydrocarbon gas, natural gas for example, in regulated amounts with a high velocity, highly turbulent blast flame containing oxygen substantially in excess of that required for complete combustion of the blast gases. This blast gas is primarily for heating the pyrolysis of a secondary “make gas” of a hydrocarbon gas that is introduced into the heated chamber in quantities far in excess of the available oxygen, so that a pyrolysis reaction occurs instead of combustion.
Brownlee et al. (U.S. Pat. No. 1,478,730) discloses a method for the production of a special carbon black from hydrocarbon feedstocks that results in enhanced yields, forming the carbon particles by pyrolysis of the hydrocarbons in the gas stream (not by combustion) and rapidly cooling the gases to separate the special carbon black before it comes into contact with the regular carbon black that forms on the furnace refractory and other surfaces in the combustion zone. Brownlee claims this special carbon black as a proprietary invention.
Bourdeau et al. (U.S. Pat. No. 3,378,345) discloses a method for growing pyrolytic graphite whiskers as elongated crystals growing perpendicular to a substrate using hydrocarbon gases with non-stoichiometric quantities (50:1 ratio of hydrocarbon gas to water or carbon dioxide) of either water or carbon dioxide or a mixture thereof. The reaction occurs at low pressures (0.1 mm to 20 mm mercury) and starts at temperatures of 799° C. to 1200° C. gradually ramping (3° C. per minute) to at least 1400° C.
Diefendorf (U.S. Pat. No. 3,172,774) discloses methods for depositing pyrolytic graphite on a composite article using a low pressure (0.2 cm to 70 cm mercury) at 1450° C. to 2000° C., using a hydrocarbon gas. The low pressure is important in allowing the carbon to form on the surface of the composite article in preference to forming soot in the gas phase.
Huang et al. (U.S. Patent Publication 2006/0269466) discloses the manufacturing of carbonaceous nanofibers using hydrocarbon as the carbon source for the carbon material.
Li et al. (U.S. Patent Publication 2008/0118426 discloses the manufacture of carbon nanotubes of varied morphology using the pyrolysis of a hydrocarbon source gas. Li does not specify they type of hydrocarbon source gas, though the specification of pyrolysis at the reaction temperatures of the description implies a hydrocarbon gas.
Fujimaki et al. (U.S. Pat. No. 4,014,980) discloses a method for manufacturing graphite whiskers based on a reaction “mixing one or more of gasified compounds having a condensed polycyclic structure of two to five benzene rings with a large amount of inert gas containing a small amount of CO, CO2 or H2O.” Fujimaki does not teach the use of the reduction reaction, the basis for the claimed methods, and does not teach the use of carbon oxides as the primary carbon source for the formation of the graphite whiskers.
Hydrocarbon pyrolysis is by definition the thermal decomposition of hydrocarbons. The present method is a departure from this art of using hydrocarbon pyrolysis in the manufacture of solid carbon products in that it uses carbon oxides as the carbon source for the formation of the various solid carbon morphologies. While the present method may use some hydrocarbon gases, such gases are used as a reducing agent for the carbon oxide gases with the secondary benefit of contributing carbon to the solid carbon product. Prior hydrocarbon pyrolysis typically does not mention or specify the importance of carbon oxides in the selective formation of the desired carbon product.
The Bosch reaction has been extensively studied, and several patents have been issued for applications of the reaction in environments where it is necessary or desirable to reclaim oxygen from respiration, for example, in a submarine or spacecraft environment. Such reclamation is generally accomplished by passing the carbon dioxide laden air through a carbon dioxide concentrator and then transferring the concentrated carbon dioxide to a carbon dioxide reduction system. A number of carbon dioxide reduction processes have been used, including both chemical and electrochemical means.
Holmes et al. in “A Carbon Dioxide Reduction Unit Using Bosch Reaction and Expendable Catalyst Cartridges” (Convair Division of General Dynamics Corporation, prepared for Langley Research Center, November 1970), discloses the use of the Bosch reaction for recovery of oxygen from carbon dioxide.
Birbara et al. (U.S. Pat. No. 4,452,676) discloses a method of recovering oxygen from carbon dioxide using the Sabatier reaction to hydrogenate the carbon dioxide to methane and water and subsequently pyrolysis the methane and deposit the resulting solid carbon on a non-catalytic glass substrate. The methane is pyrolyzed over a high temperature stable glass surface heated to about 1000° C. to 1200° C. to produce hydrogen gas and a high density carbon, i.e., having a density greater than about 2 grams per cubic centimeter. This results in lessening of the storage problem for the carbon material because of its high density. The hydrogen gas produced is also recycled back to the incoming carbon dioxide for reaction.
NASA has sponsored research into the Bosch Reaction at various times with the view to using this process to recover oxygen from respiratory CO2 in space ships. This work resulted in a series of reports, published papers, and dissertations. This work was focused on the production of water for oxygen recovery.
Selected documents related to the NASA sponsored research on the Bosch reaction include:                A carbon dioxide reduction unit using Bosch reaction.        Methods of Water Production, a survey of methods considered for the ISS including Bosch and Sabatier reactions, Oregon State University.        Comparison of CO2 Reduction Process—Bosch and Sabatier, SAE International, July 1985, Document Number 851343.        Bunnel, C. T., Boyda, R. B., and Lee, M. G., Optimization of the Bosch CO2 Reduction Process, SAE Technical Paper Series No. 911451, presented 21st International Conference on Environmental Systems, San Francisco, Calif., Jul. 15-18, 1991.        Davenport, R. J.; Schubert, F. H.; Shumar, J. W.; Steenson, T. S., Evaluation and characterization of the methane-carbon dioxide decomposition reaction, Accession Number: 75N27071.        Noyes, G. P., Carbon Dioxide Reduction Processes for Spacecraft ECLSS: A Comprehensive Review, SAE Technical Paper Series No. 881042, Society of Automotive Engineers, Warrendale, Pa., 1988.        Arlow, M., and Traxler, G., CO2 Processing and O2 Reclamation System Selection Process for Future European Space Programmes, SAE Technical Paper Series No. 891548, Society of Automotive Engineers, Warrendale, Pa., 1989.        Optimization of the Bosch CO2 Reduction Process SAE International, July 1991, Document Number 911451.        Garmirian, J. E., “Carbon Deposition in a Bosch Process Using a Cobalt and Nickel Catalyst,” Dissertation, MIT, March 1980.        Garmirian, J. E., Reid, R. C., “Carbon Deposition in a Bosch Process Using Catalysts Other than Iron,” Annual Report, NASA-AMES Grant No. NGR22-009-723, Jul. 1, 1978.        Garmirian, J. E., Manning, M. P., Reid, R. C., “The use of nickel and cobalt catalysts in a Bosch reactor,” 1980.        Heppner, D. B.; Hallick, T. M.; Clark, D. C.; Quattrone, P. D., Bosch—An alternate CO2 reduction technology, NTRS Accession Number: 80A15256.        Heppner, D. B.; Wynveen, R. A.; Schubert, F. H., Prototype Bosch CO2 reduction subsystem for the RLSE experiment, NTRS Accession Number: 78N15693.        Heppner, D. B.; Hallick, T. M.; Schubert, F. H., Performance characterization of a Bosch CO sub 2 reduction subsystem, NTRS Accession Number: 80N22987.        Holmes, R. F.; King, C. D.; Keller, E. E., Bosch CO2 reduction system development, NTRS Accession Number: 76N22910.        Holmes, R. F.; Keller, E. E.; King, C. D., A carbon dioxide reduction unit using Bosch reaction and expendable catalyst cartridges, General Dynamics Corporation, 1970, NTRS Accession Number: 71N12333.        Holmes, R. F., Automation of Bosch reaction for CO2 reduction, NTRS Accession Number: 72B10666.        Holmes, R. F.; Keller, E. E.; King, C. D., Bosch CO2 reduction unit research and development. NTRS Accession Number: 72A39167.        Holmes, R. F.; King, C. D.; Keller, E. E., Bosch CO2 reduction system development, NTRS Accession Number: 75N33726.        King, C. D.; Holmes, R. F., A mature Bosch CO2 reduction technology, NTRS Accession Number: 77A19465.        Kusner, R. E., “Kinetics of the Iron Catalyzed Reverse Water-Gas Shift Reaction”, PhD Thesis, Case Institute of Technology, Ohio (1962).        Isakson, W. E., Snacier, K. M., Wentrcek, P. R., Wise, H., Wood, B. J. “Sulfur Poisoning of Catalysts”, SRI, for US ERDA, Contract No. E(36-2)-0060, SRI Project 4387, 1977.        Manning, M. P., Garmirian, J. E., Reid, R. C., “Carbon Deposition Studies Using Nickel and Cobalt Catalysts”, Ind. Eng. Chem. Process Des. Dev., 1982, 21, 404-409.        Manning, M. P.; Reid, R. C., Carbon dioxide reduction by the Bosch process, NTRS Accession Number: 75A40882.        Manning, M. P., “An Investigation of the Bosch Process”, MIT Dissertation (1976).        Manning, M. P.; Reid, R. C.; Sophonpanich, C., Carbon deposition in the Bosch process with ruthenium and ruthenium-iron alloy catalysts, NTRS Accession Number: 83N28204.        Meissner, H. P.; Reid, R. C., The Bosch process, NTRS Accession Number: 72A39168.        Minemoto, M., Etoh, T., Ida, H., Hatano, S., Kamishima, N., and Kita, Y., Study of Air Revitalization System for Space Station, SAE Technical Paper Series No. 891576, Society of Automotive Engineers, Warrendale, Pa., 1989.        Otsuji, K., Hanabusa, O., Sawada, T., Satoh, S., and Minemoto, M., “An Experimental Study of the Bosch and the Sabatier CO2 Reduction Processes”, SAE Technical Paper Series No. 871517, presented 17th Intersociety Conference on Environmental Systems, Seattle, Wash., July 1987.        Ruston, W. R., Warzee, M., Hennaut, J. Waty, J., “The Solid Reaction Products of the Catalytic Decomposition of Carbon Monoxide on Iron at 550 C.”, Carbon, 7, 47 (1969).        Ruston, W. R., Warzee, M., Hennaut, J., Waty, J., “Basic Studies on the Growth of Carbon Deposition from Carbon Monoxide on a Metal Catalyst”, D. P. Report 394, Atomic Energy Establishment, Winfrith (1966).        Sacco, A., “An Investigation of the Reactions of Carbon Dioxide, Carbon Monoxide, Methane, Hydrogen, and Water Over Iron, Iron Carbides, and Iron Oxide”, PhD Thesis, MIT (1977).        Sacco, A., “An Investigation of the Reactions of Carbon Dioxide, Carbon Monoxide, Methane, Hydrogen, and Water over Iron, Iron Carbides, and Iron Oxide”, PhD Thesis, MIT (1977).        Sophonpanich, C., Manning, M. P., and Reid, R. C., Utilization of Ruthenium and Ruthenium-Iron Alloys as Bosch Process Catalysts, SAE Technical Paper Series No. 820875, Society of Automotive Engineers, Warrendale, Pa., 1982.        Schubert, F. H.; Clark, D. C.; Quattrone, P. D., Integrated testing of an electrochemical depolarized CO2 concentrator/EDC/ and a Bosch CO2 reduction sub system/BRS/, NTRS Accession Number: 77A19483.        Schubert, F. H.; Wynveen, R. A.; Hallick, T. M., Integration of the electrochemical depolarized CO2 concentrator with the Bosch CO2 reduction subsystem, NTRS Accession Number: 76N22907.        Wagner, Robert C.; Carrasquillo, Robyn; Edwards, James; Holmes, Roy, Maturity of the Bosch CO2 reduction technology for Space Station application, NTRS Accession Number: 89A27804, SAE Technical Paper Series No. 88099.        Global Warming & Greenhouse Gases: Integrated-Technologies Remediation of Greenhouse Gas Effects.        Walker, P. L., Rakszawski, J. F., and Imperial, G. R., Carbon Formation from Carbon Monoxide-Hydrogen Mixtures over Iron Catalysts. Properties of Carbon Formed”, J. Phys. Chem., 73, 133 (1959).        
In these prior processes, the objective is the recovery of oxygen, while the solid carbon is considered to be simply a nuisance product and disposal problem. While the methods presented here use the Bosch reaction, they differ from prior methods in that the present methods are concerned with the types and quality of solid carbon that can be produced, and the methods for controlling the solid carbon morphology through the use of catalyst, gas mixtures, and process variables (e.g., temperature, pressure, and retention times) to assure economically valuable solid carbon products are produced. The present methods identify and validate the range of solid carbon products, including carbon nanotubes, that may be produced through control of the Bosch reaction.